Optical scanning apparatus and image forming apparatus

ABSTRACT

Sealability between a cover member and a transparent member of an optical scanning apparatus is improved to improve dustproof performance. An optical scanning apparatus includes an elastic member  75  for sealing a portion between a cover member  70  and a glass member  90,  the elastic member  75  being formed on the cover member  70  so as to surround an opening portion  42,  the elastic member  75  being formed from a material that differs from that of the cover member  70.  The elastic member  75  has a protrusion  75   a  that extends towards the glass member  90.  The protrusion  75   l a  fills a gap between the cover member  70  and the glass member  90  by contacting the glass member  90  and being elastically deformed.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation, and claims the benefit, of U.S.application Ser. No. 14/916,159 filed Mar. 2, 2016, which is a nationalphase application of International Patent Application No.PCT/JP2014/073033, filed on Sep. 2, 2014, which patent(s) and patentapplications are hereby incorporated by reference herein in theirentireties, and this application claims the benefit of, and priority to,Japanese Patent Application No. 2013-185206 filed Sep. 6, 2013, whichapplication is hereby incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present invention relates to dustproof measures in a housing of anoptical scanning apparatus that is used in an image forming apparatus,such as a copying machine, a printer, a facsimile machine, or amultifunction apparatus thereof.

BACKGROUND ART

As an optical scanning apparatus that is used in an electrophotographicimage forming apparatus, an optical scanning apparatus having thefollowing structure is well known. That is, in the optical scanningapparatus, a light beam that is emitted from a light source is deflectedby a rotary polygon mirror, and the deflected light beam is guided to aphotosensitive surface of a photoconductor by an optical component, suchas a lens and a mirror, to form a latent image on the photoconductor.FIG. 6 is a schematic view of the structural components of an opticalscanning apparatus that has hitherto been generally used. Such anoptical scanning apparatus is described in detail in the description ofembodiments below. In the optical scanning apparatus, when dirt, such asdust, adheres to the optical components in the interior of the opticalscanning apparatus, the light beam is blocked by the adhered dust, as aresult of which the light quantity of light beam on the photoconductorsurface is reduced, thereby causing changes in density to occur. Inrecent years, as a result of air pollution, the amount of chemicalsubstances and the amount of fine dust in the atmosphere having a sizethat is less than or equal to 1 μm are increasing. Therefore, areduction in image quality caused by the dirt on the optical componentis becoming a more serious problem than before.

In order to prevent the entry of, for example, dust into an opticalscanning apparatus from the outside, for example, the method for sealinga gap at an outer peripheral portion of the optical scanning apparatusby putting a foaming member in the gap, or the method for placing a tapeover the gap is often carried out. However, due to, for example, thereasons described below, it is necessary to further improve sealability.In order to meet the recent demand for increasing image forming speed,the rotation speed of the rotary polygon mirror needs to be higher thanthose of existing products. The rotary polygon mirror that is set in theoptical scanning apparatus generates air current by rotating at a highspeed. Wind flows in fine spaces that connect the insides ofcontinuously connected air bubbles or places where foaming materials areaffixed. At a certain location, air flows from the inside to theoutside, and, at another location, air flows from the outside to theinside. The air that flows from the outside to the inside contains finedust that contaminates the optical component. Therefore, the more thedevice is operated, the greater the amount of fine dust that enters theinside of the optical scanning apparatus. Consequently, the dust adheresto the surface of the optical component and the inside of a housing. Inparticular, dust contained in the air current around the rotary polygonmirror adheres to a reflecting surface of the rotary polygon mirror thathas rotated at a high speed. That is, the rotation of the rotary polygonmirror causes a Karman vortex and air turbulence to be generated in thevicinity of the reflecting surface of the rotary polygon mirror, as aresult of which the air current carrying the dust collides violentlywith the reflecting surface. As a result, the fine dust that collideswith the reflecting surface of the rotary polygon mirror accumulates,and portions of the reflecting surface with which the air currentfrequently collides become dirty first. Therefore, the reflectivity atthe dirty portions of the reflecting surface is reduced. In addition,such a reduction in the reflectivity caused by the dirt reduces thelight quantity of light beam that is guided to the photoconductors, as aresult of which the density of output images is reduced.

In the optical scanning apparatus, in order to guide the light beamdeflected in the optical scanning apparatus to the photoconductor, anopening portion for sending out the light beam from the inside of theoptical scanning apparatus to the outside of the optical scanningapparatus is needed. Therefore, the optical scanning apparatus alwayshas the opening portion for allowing the light beam to exit to theoutside of the optical scanning apparatus. At the opening portion, inorder to prevent contamination such as that described above, primarily,a glass member is attached to the opening portion with a double-sidedtape. For example, Patent Literature 1 proposes a structure for bondingand securing part of the glass member to a housing.

CITATION LIST Patent Literature

PTL 1: Japanese Patent Laid-Open No. 05-080268

SUMMARY OF INVENTION Technical Problem

However, the structure that uses the double-sided tape as in PatentLiterature 1 has the following problem. That is, since a dustproof glassmember and a cover member are bonded and secured to each other with athin member, such as the double-sided tape, when warping or the like ofthe cover member occurs, a location where the tape and the cover membercannot contact each other or a location where the tape and the glassmember cannot contact each other exists, that is, a gap is formed. Inaddition, since the cover member has a large opening portion foremission, it is difficult to increase its rigidity as in the case of thehousing. Therefore, temporal deformation during, for example, transport,causes, for example, peeling of the double-sided tape. In the bondingmethod that is described in Patent Literature 1, since the glass issecured with an adhesive having a hardness of 60 or greater, thedifference between the linear expansion of the glass and the linearexpansion of the housing, a resin material being primarily usedtherefor, may cause distortion to occur when the temperature changes.Further, since the adhesive is not applied to the entire portion wherethe housing and the glass contact each other, not only is it difficultto completely eliminate the gap, but also the surface of the glassmember through which a light beam passes may become dirty due to, forexample, stringiness when the adhesive is applied to the glass member.

The present invention is achieved based on such a situation. It is anobject of the present invention to make it possible to improvesealability between a cover member and a transparent member of anoptical scanning apparatus to improve dustproof performance.

Solution to Problem

To solve the above-described problems, the present invention has thefollowing structure.

(1) An optical scanning apparatus comprises a light source that emits alight beam; a rotary polygon mirror that deflects the light beam emittedfrom the light source such that a photoconductor is scanned with thelight beam; an optical member that guides the light beam deflected bythe rotary polygon mirror to the photoconductor; a housing thataccommodates the rotary polygon mirror and the optical member therein; acover member that has an opening portion for allowing the light beam toexit to an outside from an inside of the housing; and a transparentmember that is mounted on the cover member to cover the opening portion,wherein the optical scanning apparatus includes an elastic member forsealing a portion between the cover member and the transparent member,the elastic member being molded on the cover member so as to surroundthe opening portion, the elastic member being molded from a materialthat differs from that of the cover member, wherein the elastic memberhas a protrusion that extends towards the transparent member, andwherein the protrusion fills a gap between the cover member and thetransparent member by contacting the transparent member and beingelastically deformed.

(2) An image forming apparatus comprises a photoconductor; the opticalscanning apparatus according to (1) that irradiates the photoconductorwith the light beam and forms an electrostatic latent image; developingmeans for developing the electrostatic latent image formed by theoptical scanning apparatus and forming a toner image; and transferringmeans for transferring the toner image formed by the developing means toa recording medium.

Advantageous Effects of Invention

According to the present invention, it is possible to improvesealability between the cover member and the transparent member of theoptical scanning apparatus to improve dustproof performance.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic structural view for giving a general descriptionof image forming apparatuses according to first to third embodiments.

FIG. 2 is a schematic structural view and an enlarged perspective viewof an entire optical scanning apparatus according to the firstembodiment.

FIG. 3 is a schematic view illustrating the locations where elasticmembers according to the first embodiment are set.

FIG. 4 is a schematic view illustrating a structure for improvingdustproof performance according to the first embodiment.

FIG. 5 is a schematic view illustrating an elastic member according to asecond embodiment.

FIG. 6 is a schematic structural view showing the structure of anexisting optical scanning apparatus.

DESCRIPTION OF EMBODIMENTS

Forms for carrying out the present invention are hereunder described inmore detail by way of embodiments. First, the structure of an existingoptical scanning apparatus is described. Then, the embodiments aredescribed.

Structure of Existing Optical Scanning Apparatus

FIG. 6 schematically shows structural components of an existing opticalscanning apparatus. The optical scanning apparatus that formselectrostatic latent images by applying a light beam to photoconductorincludes a rotary polygon mirror 412, which is a deflector, a motor unit41 that rotates the rotary polygon mirror 412, and optical members. Theoptical members include a collimator lens 43 and a cylindrical lens 44that shape a light beam incident upon the motor unit 41. The opticalmembers also include one or more fθ lenses (hereunder referred to as“optical lenses”) 45 for causing the light-beam scanning speed at eachphotoconductor to be uniform and a reflecting mirror 46 that guides thelight beam to the photoconductor. At the motor unit 41, the rotarypolygon mirror 412 having multiple reflecting mirror surfaces at itsouter periphery is rotated at a high speed to cause the incident lightbeam to be deflected such that each photoconductor is scanned with thelight beam.

The light quantity of the light beam that is guided to luminous bodiesis closely related to image density. Unintended changes in the lightquantity causes the density of an image formed on a recording sheet(recording medium) to be “low” or “high”. In particular, when dirt, suchas dust, adheres to the optical components in the optical scanningapparatus, the adhered dust blocks the light beam. Therefore, the lightquantity of the light beam that is guided to the photoconductor isreduced, as a result of which the density is reduced. As describedabove, a reduction in image quality caused by contamination of theoptical components by fine dust having a size less than or equal to 1 μmis becoming a problem. Ordinarily, the optical components, which arestructural components of the optical scanning apparatus, areaccommodated in a housing for protecting the optical components fromsubstances that contaminate such optical components. In the descriptionbelow, the direction of a rotation axis of a rotary polygon mirror 412at a motor unit 41 is a Z axis direction; a main scanning direction,which is a light-beam scanning direction, or a longitudinal direction ofa reflecting mirror 46 is a Y axis direction; and a direction that isperpendicular to the Y axis and the Z axis is an X axis direction.

First Embodiment Image Forming Apparatus

The structure of an image forming apparatus according to a firstembodiment is described. FIG. 1 is a schematic structural view of theentire structure of a tandem color laser beam printer according to theembodiment. The laser beam printer (hereunder simply referred to as the“printer”) includes four image forming engines 10Y, 10M, 10C, and 10Bk(illustrated by alternate long and short dashed lines) for forming tonerimages of corresponding colors, yellow (Y), magenta (M), cyan (C), andblack (Bk). The printer includes an intermediate transfer belt 20 towhich the toner images are transferred from the image forming engines10Y, 10M, 10C, and 10Bk. In addition, the printer is formed so as toform a full-color image by transferring the toner images superimposedupon and transferred to the intermediate transfer belt 20 to a recordingsheet P, which is a recording medium. The symbols Y, M, C, and Bk thatdenote the corresponding colors are hereunder omitted unless thesesymbols need to be used.

The intermediate transfer belt 20 is an endless belt, and is woundaround a pair of belt transport rollers 21 and 22. The intermediatetransfer belt 20 is formed such that the toner images formed at theimage forming engines 10 for the corresponding colors are transferred tothe intermediate transfer belt 20 while the intermediate transfer belt20 rotates in the direction of arrow B. A second transfer roller 65 isdisposed at a location where the second transfer roller 65 opposes thebelt transport roller 21 with the intermediate transfer belt 20 beinginterposed therebetween. The recording sheet P is inserted between thesecond transfer roller 65 and the intermediate transfer belt 20 thatpress-contact each other, so that the toner images are transferred fromthe intermediate transfer belt 20. The above-described four imageforming engines 10Y, 10M, 10C, and 10Bk are disposed side by side belowthe intermediate transfer belt 20, so that the toner images formed inaccordance with pieces of image information concerning the correspondingcolors are transferred to the intermediate transfer belt 20 (hereunderreferred to as “first transfer”). These four image forming engines 10are such that the image forming engine 10Y for yellow, the image formingengine 10M for magenta, the image forming engine 10C for cyan, and theimage forming engine 10Bk for black are disposed in that order along therotation direction of the intermediate transfer belt 20 (the directionof arrow B).

An optical scanning apparatus 40 that exposes photoconductor drums 50,which are photoconductors, of the corresponding image forming engines 10in accordance with pieces of image information is disposed below theimage forming engines 10. The optical scanning apparatus 40 is anoptical scanning apparatus that is common to all of the image formingengines 10Y, 10M, 10C, and 10Bk, and includes four semiconductor lasers(not shown) that emit laser beams modulated in accordance with pieces ofimage information concerning the corresponding colors. The opticalscanning apparatus 40 includes the rotary polygon mirror 412 thatdeflects the light beams such that each photoconductor drum 50 isscanned with the corresponding light beam along the axis direction ofthe photoconductor drum 50 (the Y axis direction), and the motor unit 41that rotates the rotary polygon mirror 412. Each light beam deflected bythe rotary polygon mirror 412 is guided to the optical members in theoptical scanning apparatus 40, exits from each opening portion 42 to theoutside of the optical scanning apparatus 40, and is guided to eachphotoconductor drum 50, so that each photoconductor drum 50 is exposedto the corresponding light beam.

Each image forming engine 10 includes the photoconductor drum 50 and acharging roller 12 that charges the photoconductor drum 50 to a uniformbackground potential. In addition, each image forming engine 10 includesa developing unit 13 that forms a toner image by developing anelectrostatic latent image formed on the corresponding photoconductordrum 50 by exposing the corresponding photoconductor drum 50 to thelight beam. The developing units 13 form the toner images in accordancewith the pieces of image information concerning the corresponding colorson the corresponding photoconductor drums 50. First transfer rollers 15are disposed at locations opposing the photoconductor drums 50 of thecorresponding image forming engines 10 such that the intermediatetransfer belt 20 is interposed between the first transfer rollers 15 andthe corresponding photoconductor drums 50. By applying predeterminedtransfer voltage to the first transfer rollers 15, the first transferrollers 15 transfer the toner images on the corresponding photoconductordrums 50 to the intermediate transfer belt 20.

The recording sheet P is supplied into the printer from a sheet-feedingcassette 2 that is accommodated at a lower portion of a printer housing1, more specifically, to a second transfer position where theintermediate transfer belt 20 and the second transfer roller 65 contacteach other. A sheet-feeding roller 25 and a pickup roller 24 for takingout recording sheets P accommodated in the sheet-feeding cassette 2 areprovided side by side with each other above the sheet-feeding cassette2. A retard roller 26 that prevents double feeding of the recordingsheets P is disposed at a location where the retard roller 26 opposesthe sheet-feeding roller 25. A transport path 27 for transporting therecording sheets P in the printer is substantially perpendicularlyprovided along a right side face of the printer housing 1. The recordingsheet P that has been taken out from the sheet-feeding cassette 2 thatis positioned at a bottom portion of the printer housing 1 moves upwardin the transport path 27, and is sent to registration rollers 29 thatcontrol the timing in which the recording sheet P moves to the secondtransfer position. Thereafter, after the toner images have beentransferred to the recording sheet P at the second transfer position,the recording sheet P is sent to a fixing unit 3 (illustrated by abroken line) that is provided at a downstream side in a transportdirection. Then, the recording sheet P to which the toner images havebeen fixed by the fixing unit 3 passes between discharging rollers 28,and is discharged to a sheet-discharging tray la provided at an upperportion of the printer housing 1.

In order to form a full-color image by the color laser beam printerhaving such a structure, first, the optical scanning apparatus 40exposes the photoconductor drums 50 of the corresponding image formingengines 10 at a predetermined timing in accordance with the pieces ofimage information concerning the corresponding colors. This causes thelatent images that are in accordance with the pieces of imageinformation to be formed on the photoconductor drums 50 of thecorresponding image forming engines 10. Here, in order to obtain goodimage quality, it is necessary for the latent images that are formed bythe optical scanning apparatus 40 to be reproduced precisely atpredetermined locations on the corresponding photoconductor drums 50,and the light quantity of the light beams for forming the latent imagesto always consistently be desired values.

Structure of Optical Scanning Apparatus

FIG. 2(a) is a schematic structural perspective view of the structure ofthe optical scanning apparatus according to the embodiment. FIG. 2(b) isan enlarged perspective view of a circled portion A in FIG. 2(a). Alight source unit, a deflector (see FIG. 6), optical lenses 45, and thereflecting mirror 46 are disposed in the interior or at an outerperipheral portion of the optical scanning apparatus 40. A light sourcethat emits a light beam is mounted on the light source unit. Thedeflector (the rotary polygon mirror 412 and the motor unit 41) (seeFIG. 6) reflects/deflects the light beam. The optical lenses 45 and thereflecting mirror 46 (see FIG. 6) are optical members required forguiding the light beam to a surface to be scanned and forming images.Each elastic member 75 (dark portion that is black in the figure) isintegrally formed with a cover member 70. The cover member 70 is set ona top portion of a housing 85, for example, by a snap-fit method or by asecuring method using screws. In the embodiment, the cover member 70 issecured to the housing 85 by engaging snap-fit portions 88 with snap-fitengagement portions 87.

Each elastic member 75 is formed as follows. That is, after the covermember 70 has been molded, the cover member 70 is reset in a differentmold, to perform, for example, insert molding or outsert molding foradditionally molding each elastic member 75. Each elastic member 75 haslow heat capacity, and tends to be cooled and hardened. Therefore, bypouring the material of each elastic member 75 that has been melted ataround 100° C. into the mold by the insert molding or the outsertmolding, it is possible to integrally form each elastic member 75 andthe cover member 70 with each other without deforming by heat the covermember 70 that has been previously molded. Even in the embodiment, thematerial of each elastic member 75 that has been melted at 120° C. ispoured with respect to the cover member 70 formed from ABS resin.Immediately after each elastic member 75 has come into contact with thecover member 70, each elastic member 75 is suddenly cooled and hardened,as a result of which it is possible to integrate each elastic member 75with the cover member 70 without deforming the cover member 70. In thisway, by molding each elastic member 75 by using the mold, advantagessuch as those mentioned below can be provided. That is, each glassmember 90, which is a dustproof transparent member, is placed on thecover member 70 with each elastic member 75 being interposedtherebetween so as to cover light-beam exiting opening portions 42(hereunder referred to as the “opening portions 42”). Each elasticmember 75 may be formed by two-color molding in which each elasticmember 75 and the cover member 70 formed from a different material areintegrally molded with each other. In addition, although, in theembodiment, the transparent members that cover the light-beam openingportions 42 are described as being the glass members 90, the transparentmembers are not limited thereto. In other words, the members that coverthe light-beam opening portions 42 only need to be transparent members,so that they may be made of, for example, plastic.

Each glass pressing member 92 has a hole 921 (illustrated by a brokenline). The glass pressing members 92 are set such that protrusions 93 ofthe cover member 70 engage with the holes 921, and are secured bypressing such that the glass members 90 do not fall off. Morespecifically, the protrusions 93 are inserted into the holes 921, andthe glass pressing members 92 are moved in a longitudinal direction (−Yaxis direction) to engage the protrusions 93 with the glass pressingmembers 92. Each glass pressing member 92 has a slit portion 922.Protrusions 94 of the cover member 70 that are provided for the slitsare inserted into the slits 922, and the glass pressing members 92 aremoved in the longitudinal direction (−Y axis direction) to engage theprotrusions 94 that are provided for the slits with the glass pressingmembers 92. This secures the glass pressing members 92 by pressingwithout allowing the glass members 90 to fall off. Here, FIG. 3 is aschematic view of the cover member 70 according to the embodiment whenseen from the top (+side in the Z axis direction). Each elastic member75 is disposed at a region 91, which is illustrated by a broken line inFIG. 3, so as to be formed continuously with an outer peripheral portionof the corresponding opening portion 42 that is provided in the covermember 70. Each elastic member 75 is formed in the shape of a continuousframe even at a location where the elastic member 75 contacts thecorresponding glass member 90. Each elastic member 75 has a sufficientthickness that allows it to be elastically deformed so as to contact anuneven surface of the cover member 70 and an uneven surface of thecorresponding glass member 90 without a gap. This allows each elasticmember 75 to fill a portion between the cover member 70 and each glassmember 90, so that it is possible to considerably improve dustproofperformance. By the glass pressing members 92, the glass members 90 arepressed from thereabove against the cover member 70. That is, the glassmembers 90 are pressed in a −Z axis direction in FIG. 2 against thecover member 70 by the glass pressing members 92. Therefore, even if atleast one of the cover member 70, the glass member 90, and the glasspressing member 92, for example, expands or contracts due to, forexample, environmental changes, it is possible to achieve stablesealability (hermeticity).

Function of Elastic Members 75

FIG. 4 is a sectional structural view illustrating a structure forimproving dustproof performance according to the embodiment. FIG. 4(a)is a sectional view when the optical scanning apparatus 40 is cut awayby a plane that is parallel to an XZ plane including the protrusions 93in FIG. 2. More specifically, FIG. 4(a) illustrates, in a sectional viewtaken along line D-D (alternate long and short dashed line) in FIG.2(a), a cross section of the leftmost opening portion 42 among the fouropening portions 42 along the cross section. In a cross section takenalong line E-E (alternate long and short dashed line) in FIG. 2(a), thelength of each opening portion 42 in the Y-axis direction becomes long,but the structure near each elastic member 75 described below is similarto that in the sectional view taken along line D-D. FIG. 4(b) onlyillustrates the elastic member 75 and the glass member 90 shown in FIG.4(a).

Cover Member

The cover member 70 has the opening portions 42 for allowing the lightbeams to exit from the inside of the optical scanning apparatus 40 tothe outside. As illustrated in FIG. 3, the elastic members 75 arecontinuously disposed with the cover member 70 at the regions 91, whichare illustrated by dotted lines, at outer peripheral portions of theopening portions 42. A cross section of the cover member 70 where anelastic member 75 is disposed has a C shape formed by surfaces 70 b to70 d in FIG. 4(a), and the elastic member 75 is formed in a C-shapedrecessed portion by the above-described method.

Each surface 70 b that is parallel to an XY plane of the C-shapedrecessed portion of the cover member 70 contacts a surface 75 b of thecorresponding elastic member 75 described below. Of the two surfaces 70c and 70 d that are parallel to a YZ plane of the C-shaped recessedportion of the cover member 70, the surface 70 c contacts a surface 75 cof its corresponding elastic member 75, and the surface 70 d contacts asurface 75 d of its corresponding elastic member 75 described below.Each surface 70 c is a surface that is closer to the opening portion 42with reference to a protrusion 75 a of the elastic member 75 describedbelow, and each surface 70 d is a surface that is farther away from theopening portion 42 with reference to the protrusion 75 a of the elasticmember 75 described below.

Protrusions of Elastic Members

The elastic members 75 each include the protrusion 75 a that protrudesin the +Z axis direction. As illustrated in FIG. 4(b) (i), the shape ofa cut surface of each protrusion 75 a (hereunder simply referred to asthe “sectional shape”) formed by cutting each protrusion 75 a by a planethat is parallel to the XZ plane is a trapezoidal shape. The sectionalshape of the protrusion 75 a of each elastic member 75 is such that itslength in the X axis direction becomes smaller in the +Z axis direction.As shown in FIG. 4(a), an end of the protrusion 75 a of each elasticmember 75 is formed so as to contact a surface of the glass member 90facing the cover member 70, the glass member 90 having moved in thedirection of arrow W (−Z axis direction) from the top of FIG. 4(a). Thatis, when each glass member 90 is set on the cover member 70, theprotrusion 75 a of each elastic member 75 is a portion of the elasticmember 75 that contacts this surface of the glass member 90 facing thecover member 70 first.

Accordingly, the contact portion of each elastic member 75 is aprotruding portion, such as the protrusion 75 a. By minimizing the areaof contact with each glass member 90, it is possible to reduce the forcethat each glass member 90 receives from its corresponding elastic member75 when each glass member 90 is set. By minimizing the area of contactbetween the protrusion 75 a of each elastic member 75 and itscorresponding glass member 90, it is possible to mitigate the problem inwhich light paths of the light beams are changed as a result of eachglass member 90 being deformed by the force that it receives from itscorresponding elastic member 75 when it is set. Here, a structure inwhich the elastic members 75 do not have the protrusions 75 a will bedescribed. In the structure in which the elastic members 75 do not havethe protrusions 75 a, the entire surface of each elastic member 75 thatfaces its corresponding glass member 90 contacts the corresponding glassmember 90. Here, compared to the case in which the elastic members 75each have the protrusion 75 a according to the embodiment, each glassmember 90 receives a large elastic force from its corresponding elasticmember 75. In addition, the elastic force that is received from eachelastic member 75 is not uniform along the longitudinal direction. As aresult, the thickness of each glass member 90 along the longitudinaldirection is no longer uniform, as a result of which each glass member90 is deformed so as to be twisted. The deformation that has occurred ineach glass member 90 changes the light paths of the light beams asdescribed above.

By reducing the rigidity of the contact portion (the protrusion 75 a) ofeach elastic member 75 with its corresponding glass member 90, that is,by forming the contact portions from elastic materials, it is possibleto achieve good shape transferability with respect to the fineirregularities on the surface of each glass member 90. That is, sincethe protrusions 75 a are formed from elastic materials, even if thesurface of each glass member 90 that faces the cover member 70 isuneven, each protrusion 75 a is deformed into a shape that is incorrespondence with the unevenness. Therefore, the uneven surface ofeach glass member 90 can be filled with its corresponding elastic member75. Consequently, when setting each glass member 90 on the openingportion 42 in the cover member 70, it is possible to improve thesealability (hermeticity) between each glass member 90 and the covermember 70.

Here, the area of contact of each elastic member 75 with itscorresponding glass member 90 is smaller than the area of contact ofeach elastic member 75 with the cover member 70. The area of contact ofeach elastic member 75 with the cover member 70 is, as shown in FIG.4(b), equal to the sum of the area of the surface 75 b of the elasticmember 75, which is a surface that is parallel to the XY plane, and theareas of the surfaces 75 c and 75 d of the elastic member 75, which aretwo surfaces that are parallel to the YZ plane. Here, each surface 75 cis a surface that is closer to the opening portion 42 with reference tothe protrusion 75 a of the elastic member 75, and each surface 75 d is asurface that is farther away from the opening portion 42 with referenceto the protrusion 75 a of the elastic member 75. On the other hand, thearea of contact of each elastic member 75 with its corresponding glassmember 90 is an area when the glass member 90 is pressed by itscorresponding glass pressing member 92, that is, when the glass member90 is set on the cover member 70. In the embodiment, such a structure isused to prevent any of the elastic members 75 bonded to thecorresponding glass members 90 from being removed from the cover member70 together with the corresponding glass members 90 when the glassmembers 90 are removed and replaced as a result of being scratched, etc.

Grooves in Elastic Members

Grooves 75 j are provided beside the corresponding protrusions 75 a ofthe elastic members 75. More specifically, the grooves 75 j in thecorresponding elastic members 75 are provided farther away from thecorresponding opening portions 42 than the protrusions 75 a of thecorresponding elastic members 75 are. That is, the grooves 75 j in theelastic members 75 are provided in regions situated outwardly of theprotrusions 75 a. In other words, when viewed from an upper surface ofthe cover member 70 (+side in the Z axis direction), the grooves 75 jare provided such that rectangular regions formed by the grooves 75 j inthe elastic members 75 are wider than rectangular regions formed by theprotrusions 75 a of the elastic members 75. By such a structure, asshown in FIG. 4(b) (ii), when the elastic members 75 are pressed by theglass members 90 when the glass members 90 are set, the protrusions 75 aare squashed by the glass members 90, and are considerably deformed andmoved in the direction of arrow C, that is, towards the grooves 75 j. Asa result of the deformation and movement of the protrusions 75 a of theelastic members 75, the pressing force from the glass members 90 isabsorbed by the elastic members 75. Therefore, the pressing forcetowards the cover member 70 is reduced, so that it is possible toconsiderably reduce the repulsive force of the cover member 70 withrespect to the glass members 90. This makes it possible to, withdustproof performance being improved, further prevent, for example,deformation of the glass members 90 caused by the repulsive force.

As described above, the grooves 75 j are provided farther away from theopening portions 42 than the protrusions 75 a are. That is, theprotrusions 75 a are provided between the opening portions 42 and thecorresponding grooves 75 j. Therefore, if the protrusions 75 a of theelastic members 75 are deformed when the glass members 90 are set on thecover member 70, the protrusions 75 a can be set so as to move away fromthe opening portions 42. Each elastic member 75 is formed from a rubbermaterial (that differs from that of the cover member 70), such as a hotmelt material or an elastomer material. Such materials are viscous. Whenthe elastic members 75 are exposed, dust or the like that floats in theair adheres to the elastic members 75. For example, when the grooves 75j in the elastic members 75 are provided closer to the opening portions42 than the protrusions 75 a are, the protrusions 75 a are set so as tomove towards the opening portions 42. In this case, the protrusions 75 aof the elastic members 75 may protrude into the corresponding openingportions 42. When the protrusions 75 a protrude into the correspondingopening portions 42, the elastic members 75 are exposed. When thegrooves 75 j are not formed in the elastic members 75, the direction ofmovement of the protrusions 75 a can no longer be set. In such a case,the protrusions 75 a of the elastic members 75 may move towards theopening portions 42, as a result of which the protrusions 75 a mayprotrude into the opening portions 42 and become exposed.

However, as described above, in the embodiment, the protrusions 75 a ofthe elastic members 75 are squashed towards the grooves 75 j, that is,away from the opening portions 42, and are reliably interposed betweenthe cover member 70 and the glass members 90. This makes it possible toalso mitigate the problem in which light beams are blocked when, forexample, dust adheres to any of the elastic members 75. Each groove 75 jaccording to the embodiment has the functions of setting the directionof movement of its corresponding protrusion 75 a when the protrusion 75a is deformed, reducing the area of contact between the elastic member75 and its corresponding glass member 90, and reducing the elastic forcefrom the elastic member 75.

In the embodiment, a synthetic-rubber based elastic member is used foreach elastic member 75. In selecting the material of each elastic member75, prevention of distortion of the device by an elastic force that istoo strong, and maintenance of the reflectivity and transmissivity forsending a sufficient quantity of light to the surfaces to be scanned areimportant. Therefore, for, for example, a softening agent that iscontained in each elastic member 75 serving as a sealing member, it isimportant to select a material that, while having low molecular weight,undergoes little outgassing and infrequently chemically attacks resin.Other types of elastic members, such as those formed from elasticmaterials that are urethane-based materials subjected to foam molding,and those formed from silicone-based elastic materials having excellentlight resistance, may be used.

According to the embodiment, it is possible to improve sealabilitybetween the cover member and the transparent members of the opticalscanning apparatus to improve dustproof performance.

Second Embodiment Shapes of Protrusions

FIG. 5 is a schematic sectional view illustrating the shape of anelastic member 75 according to a second embodiment. Similarly to FIG. 4,FIG. 5 is a sectional view when an optical scanning apparatus is cutaway by a plane that is parallel to the XZ plane including theprotrusions 93 in FIG. 2. Each elastic member 75 has a protrusion 75 a 2that extends towards the side where a glass member 90 is set. Eachprotrusion 75 a 2 according to the embodiment is formed so as to extendaway from an opening portion 42 with decreasing distance from an endthereof (that is, in the +Z axis direction). As shown in FIG. 5(a), anangle θ between a surface 75 a 21 of each protrusion 75 a 2 that is faraway from the opening portion 42 and a surface 75 e of each elasticmember 75 that faces the glass member 90 is an acute angle (θ<90°). Inthis way, by forming the protrusion 75 a 2 of each elastic member 75 soas to be inclined away from the opening portion 42, the protrusion 75 a2 of each elastic member 75 falls in a direction away from the openingportion 42 and is pressed when the corresponding glass member 90 is set.That is, as also described in the first embodiment, even in thisembodiment, it is possible to prevent the problem in which light beamsare blocked when dust or the like adheres to any of the elastic members75 as a result of the protrusion 75 a 2 of the corresponding elasticmember 75 or the protrusions 75 a 2 of the corresponding elastic membersmoving towards the opening portion 42.

The protrusion 75 a 2 of each elastic member 75 is formed so as to bethin as shown in FIG. 5(a). That is, as shown in FIG. 5(a), theprotrusion 75 a 2 of each elastic member 75 is formed such that the areaof a cross section when the protrusion 75 a 2 is cut away by a planethat is parallel to the XZ plane is small. This makes it possible toalso considerably reduce the elastic force that acts upon the glassmember 90 from the protrusion 75 a 2.

Bent Portions of Protrusions

As shown in FIG. 5(b), a protrusion 75 a 3 that is formed by providingthe protrusion 75 a 2 shown in FIG. 5(a) with a bent portion 751 may beprovided. When each protrusion 75 a 3 is formed so as to have the bentportion 751, each protrusion 75 a 3 is easily bent. Therefore, it ispossible to further reduce the elastic force that acts upon the glassmembers 90 from the protrusions 75 a 3.

As described in the first embodiment, a structure including grooves thatare provided farther from the corresponding opening portions 42 than theprotrusions 75 a 2 or the protrusions 75 a 3 are may be used.

Accordingly, according to the embodiments, it is possible to improvesealability between the cover member and the transparent members of theoptical scanning apparatus to improve dustproof performance.

The present invention is not limited to the above-described embodiments,so that various changes and modifications can be made without departingfrom the spirit and scope of the present invention. Therefore, in orderto make public the scope of the present invention, the following claimsare attached.

REFERENCE SIGNS LIST

40 optical scanning apparatus

42 opening portion

70 cover member

75 elastic member

75 a protrusion

85 housing

90 glass member

1. An image forming apparatus comprising: a photoconductor; and an optical scanning apparatus configured to form an electrostatic latent image on the photoconductor, the optical scanning apparatus comprising: a light source configured to emit a light beam for forming the electrostatic latent image; a rotary polygon mirror disposed inside a frame of the optical scanning apparatus and configured to deflect the light beam emitted from the light source such that the photoconductor is scanned with the light beam; an optical member disposed inside the frame and configured to guide the light beam deflected by the rotary polygon mirror to the photoconductor; a transparent member attached to the frame; and an elastic member molded on the frame; wherein an opening, for passing the light beam deflected by the rotary polygon mirror from inside of the frame to outside of the frame, is formed on the frame and is covered by the transparent member, wherein the elastic member is molded on the frame in such a way as to enclose the opening and protrude from a fluid passage, the elastic member being made of a material that is different from a material of the frame, the elastic member being more elastic than the frame, the fluid passage being formed on the frame in such a way as to enclose the opening, a molten material of the elastic member being poured into the fluid passage so as to mold the elastic member on the frame in such a way as to enclose the opening, and wherein the elastic member elastically deforms due to contact of a protruding portion of the elastic member protruding from the fluid passage with the transparent member, and the deformed elastic member seals a gap between the frame and the transparent member.
 2. The image forming apparatus according to claim 1, wherein the protruding portion becomes thinner towards the transparent member.
 3. The image forming apparatus according to claim 1, wherein the protrusion is inclined away from the opening portion.
 4. The image forming apparatus according to claim 3, wherein the protrusion has a bent portion.
 5. The image forming apparatus according to claim 1, wherein the elastic member has a groove that is positioned farther away from the opening portion than the protrusion is.
 6. The image forming apparatus according to claim 1 further comprising a pressing member that presses the transparent member against the elastic member by engaging with the frame.
 7. The image forming apparatus according to claim 1 further comprising: a developing unit configured to develope the electrostatic latent image formed by the optical scanning apparatus and forming a toner image; and a transferring unit configured to transfer the toner image formed by the developing means to a recording medium. 